'A dinosaur dance floor'( About one-eighth of the tracks show...)

"While these impressions may be mistaken for potholes caused by weathering, close examination reveals many footprint features," Seiler says.

Dinosaur footprints are named by their shape because the animals that made them haven't been identified. Four kinds of footprints were found on the trample surface:

• Eubrontes footprints measure 10 inches to 16 inches long and have three toes and a heel. Eubrontes tracks are believed to have been made by upright-walking dinosaurs 16 to 20 feet long, or smaller than Tyrannosaurus rex.

• Grallator tracks are about 4 inches to 7 inches long, are three-toed and were left by small dinosaurs only a few feet tall.

• Sauropodomorph dinosaur tracks, which are more circular than the other types, were left by creatures that walked on four legs and were the largest dinosaurs at the site. Their tracks range from 6 inches to 11 inches long. Seiler says the tail-drag marks are associated with these circular footprints, so they likely were made by sauropods.

• Anchisauripus tracks measure 7 inches to 10 inches long and were made by dinosaurs that ranged from 6 feet to 13 feet in length.

When the footprints were made 190 million years ago, "the continents were arranged so this area was in the tropics" and was part of the supercontinent named Pangaea, says Seiler. "It was a desert, like the Sahara but much larger than the Sahara is today," covering much of Utah, Wyoming, Colorado, New Mexico, Arizona and Nevada.

"Some studies indicate winds probably were much stronger than normal because all the continents were together," says Chan. "That's why you had monster dunes."

"To support large dinosaurs, there probably wasn't just one water
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